It is possible to do run-time linking in DOS with WDOSX extender - http://michael.tippach.bei.t-online.de/wdosx/
Logged In: YES
I've had a look at WDOSX, and there is still not enough
functionality yet to make this work for Regina.
However, Regina 3.1 comes with "static" dynamic loading.
This allows you to build a Regina executable which statically
links in various Rexx extension libraries, provided the Rexx
extensions cater for being built as static libraries.
All of my Rexx extensions and Patrick McPhee's Regutil are
Logged In: YES
Maybe DXE will be better:
It has some compatibility with dlopen...
WDOSX .DLLs (IIRC) only works for PE files. Causeway has some support for .DLLs, but I've never tried. DXE2 is older than DJGPP 2.04 "beta" (Nov. 2003)'s DXE3. "current" 2.03p2 (Dec. 2001) still uses old DXE1, which is weaker. And now you even need libc from CVS if you intend to use GCC 4.5.x or newer with DXE3 (see Lua 5.2.0 port or old PythonD 2.4 port).
In fact, I'm very very green on all such things. But actually, Daniel Borca (way back in 2006) made an unofficial port of ELF / flat model / .so support to DJGPP (normally COFF, null ptr protection) with GCC 4.0.0 + BinUtils 2.16. And the whole point of my comment is this: I think I (barely) got it to actually work with REGINA.EXE (plus libregina.so, and test.c examples via dynfunc.rexx). Now I just need Regina's maintainer(s) to contact me so I can send them my (ugly) patch. :-)